Thermostatic material



@ Nov. 29, 1927. 1,650,951

x r H. D. MATTHEWS THERMOS TATI 0 MATERIAL Filed March 18, 1925 Thermalexpansion coefficient I I l l l I I 0 I00 200 500 400 500 600 700Temperarure in degrees Cenrigrade Patented Nov. 29, 1927.

UNITED STATES PATENT OFFICE.

HOWARD D. MATTHEWS, 0F EDGEWOOD, PENNSYLVANIA, ASSIGNOR TO WESTING-HOUSE ELECTRIC &; MANUFACTURING COMPANY, A CORPORATION OF PENNSYL-VANIA.

THERMOSTATIC MATERIAL.

Application filed March 18, 1925. Serial No. 16,341.

My invention relates to temperature controlled devices and particularlyto thermostatic material and bimetallic thermostats.

One object of my invention is to provide a bimetallic. thermostat, theelements of which shall have different temperature coeflicients and thatshall be composed ofmaterial capable of being subjected to relativelyhigh temperatures without substantial change of structure after repeatedoperations thereof.

In practicing my invention, I provide a bimetallic thermostatic elementcomprising two metallic elements, one of said elements being a chromiumsteel.

The single figure of the accompanying drawing illustrates two curvesshowing the relative temperature coefiicients of expansion of two metalsemployed in practicing my invention.

The use of two more or less closely united strips of metal to form abimetallic thermostatic member that is responsive to heat has long beenknown. Iron and brass have usually been employed for such purposes andwill function properly if the temperatures to which they are subjecteddo not exceed a relatively limited value. However, when it is desired tooperate at relatively high temperatures, such as from 200 to 500 or 600C. the above named metals rapidly lose their original elasticity and thedevice fails to function properly.

I have found that a thermostatic member comprising two metal elements,one of these being a chromium steel,-and used in connection with acopper-nickel alloy, generally known as Monel metal, will functionproperly at very much higher temperatures than has been heretoforethought possible.

The curve 11 shows the temperature coefiicients of expansion of acopper-nickel alloy, comprising substantially two-thirds copper andone-third nickel and generally known as Monel metal, between thetemperature range of zero to 550 C. While the curve is illustrated asbeing substantially a straight line, values may vary slightly therefrom,but the curve shows substantially correct values.

The second member of such bimetallic heat-responsive device is achromium steel comprising substantially 10 to 15% of chromium withadmixtures of phosphorus, silicon, manganese, carbon and sulphur, thelatter being present in relatively small amounts only. Curve 12illustrates the temperature coefficients of expansion of such chromiumsteel alloy up totemperatures of about 550 C. and it may be noted thatthe difference between the respective temperature coefficients ofexpansion varies but little over the entire range of temperature. Such achromium steel is not areversible alloy but the transformation pointsthereof occur at temperatures. above 750 C. In some samples that havebeen tested, these transformation points occur at about 850 C. to 950 C.Hence, it is necessary that a bimetallic heatresponsive device builtaccording tomy invention, be used at temperatures well below by weldingor riveting, and any suitable or desired construction is within thescope of my invention, which comprises more particularly the use of achromium steel alloy having an appreciable admixture of chromium whosetransformation points occur above a temperature of 750 C.'

Various modifications and changes may be made without departing from thespirit of the invention, and I desire therefore, that only suchlimitations shall be placed thereon as are imposed by the prior art.

I claim as my invention:

1. A heat responsive device consisting of two metallic elements, one ofsaid elements being an irreversible chromium steel alloy, and the otherelement being an alloy of copper and nickel.

2. A heat responsive device consisting of two metallic elements, one ofsaid elements being an irreversible chromium steel alloy, whosetransformation points occur at temperatures above 750" 1., an l theother vln ment being a copper nick l alloy cnntnlning n01 over 67% 0FTOPPQI.

3. A heat responsive derive consisting of lWO metallic elements, one ofsaid element; being steel containing 1101 over 15% of chromium. and the.other of mid elements being a copper nickel n l y m'ntnining nnl rm 67f;of Copper.

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